Enhance nox

CONTRIBUTING.md

@@ -37,6 +37,14 @@ If you want to start from scratch, use `clean`:
 nox -s clean
 ```
 
+Positional arguments given to Nox are passed over to PyTest as-is,
+which can be used to run tests selectively or bail at the first failure:
+
+```bash
+nox -s test -- -x yakut/param/formatter.py -k test_format_param
+#              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PyTest options
+```
+
 #### Running tests/linters selectively from a virtual environment created by Nox
 
 Running the full test suite using Nox takes too much time for interactive testing during development.

noxfile.py

@@ -70,20 +70,20 @@ def test(session):
         # We do it here because the sudo may ask the user for the password; doing that from the suite is inconvenient.
         session.run("sudo", "setcap", "cap_net_raw+eip", str(Path(session.bin, "python").resolve()), external=True)
 
-    # The directories to test may be overridden if needed when invoking Nox.
-    src_dirs = [(ROOT_DIR / t) for t in (session.posargs or ["yakut", "tests"])]
+    src_dirs = [(ROOT_DIR / t) for t in ["yakut", "tests"]]
 
     # Run PyTest and make a code coverage report.
-    env = {
-        "PYTHONPATH": str(DEPS_DIR),
-        "PATH": os.pathsep.join([session.env["PATH"], str(DEPS_DIR)]),
-    }
+    # Positional arguments passed to Nox after "--" are forwarded to PyTest as-is.
     session.run(
         "pytest",
         *map(str, src_dirs),
         # Log format cannot be specified in setup.cfg https://github.com/pytest-dev/pytest/issues/3062
         r"--log-file-format=%(asctime)s %(levelname)-3.3s %(name)s: %(message)s",
-        env=env,
+        *session.posargs,
+        env={
+            "PYTHONPATH": str(DEPS_DIR),
+            "PATH": os.pathsep.join([session.env["PATH"], str(DEPS_DIR)]),
+        },
     )
 
     # The coverage threshold is intentionally set low for interactive runs because when running locally